Adhesive for bonding rubber to fibers

ABSTRACT

An adhesive for bonding a nitrile group-containing highly saturated rubber to glass fibers or organic synthetic fibers, which comprises a nitrile group-containing highly saturated rubber latex having an iodine number of not more than 120 and a resoncinol/formaldehyde resin.

This is a division of application Ser. No. 07/174,866, filed Mar. 29,1988, now U.S. Pat. No. 5,017,639.

This invention relates to an adhesive for bonding a nitrilegroup-containing highly saturated rubber to glass fibers or organicsynthetic fibers such as polyester fibers or polyamide fibers, and tofibers coated with the adhesive.

In the prior art, reinforcing glass fiber cords or organic syntheticfiber cords used in timing belts, tires, rubber hoses and diaphragmshave a coating of an adhesive composed of a mixture (RFL) ofresorcinol-formaldehyde resin (RF) and a rubber latex (L). The adhesivecoating improves the adhesion of rubber to fibers.

A vinylpyridine/styrene/butadiene copolymer latex, a styrene/butadienerubber latex, a chloroprene rubber latex and a butadiene rubber latex,for example, have previously been used as the rubber latex (U.S. Pat.No. 3,591,357 and U.S. Pat. No. 3,964,950). Such conventionalrubber-reinforcing fibrous cords show good adhesion to chloroprenerubber if the fibers are glass fibers. When the fibers are organicsynthetic fibers, the fibrous cords show good adhesion to naturalrubber, styrene/butadiene copolymer rubber, acrylonitrile/butadienecopolymer rubber, etc.

In recent years, there has been an increasing demand for heat-resistantrubbers in various fields, and for example, automobile timing belts nowrequire rigorous heat resistance because of the rise in the temperatureof automobile engine rooms. Thus, the chloroprene rubber previously usedas a belt material has gradually been superseded by hydrogenated nitrilerubber (nitrile group-containing highly saturated rubber). Furthermore,the acrylonitrile/butadiene copolymer rubber as a material foroil-resistant hoses and diaphragms is also being superseded byhydrogenated nitrile rubber.

However, belts, hoses or diaphragms having the glass fiber or organicsynthetic fiber cords have a short service life because when the fibrouscords are coated with conventional adhesives composed of RFL, theadhesive coatings have insufficient heat resistance, the coated fibrouscords have a low adhesion strength with respect to hydrogenated nitrilerubber, and after heat aging, their adhesion strength is drasticallyreduced.

It is known that to improve adhesion of rubber to glass fiber cords, therubber is treated with a secondary treating agent such as rubber pastecomposed of a solution of a rubber compound in gasoline [see, forexample, Journal of Japanese Adhesion Association, vol. 7, No. 5 (1971),pages 23-29]. Since, however, the heat resistance of the secondarytreating agent has insufficient heat resistance, the defect of shortlife has not been overcome by such a secondary treatment. It wassuggested on the other hand to use an adhesive composed of RFL solutioncontaining a latex of chlorosulfonated polyethylene in an attempt toimprove the adhesion of hydrogenated nitrile rubber to organic syntheticfibrous cords (European Patent Publication No. 194,678A). Nosatisfactory results have been obtained with this adhesive.

It is an object of this invention to provide an adhesive which shows asufficient adhesion strength both at room temperature and after heataging when it is used for bonding a nitrile group-containing highlysaturated rubber to glass fibers or organic synthetic fibers.

This object is achieved in accordance with this invention by an adhesivecomprising a latex of a nitrile group-containing highly saturated rubberhaving an iodine number of not more than 120 and aresorcinol-formaldehyde resin.

In view of the film strength of rubber and the strength of adhesion torubber, the rubber constituting the nitrile group-containing highlysaturated rubber latex should have an iodine number of not more than120, preferably 0 to 100, especially preferably 0 to 80. The iodinenumber is determined in accordance with JIS K-0070.

The nitrile group-containing highly saturated rubber constituting thelatex may be, for example, a rubber obtained by hydrogenating theconjugated diene units of an unsaturated nitrile/conjugated dienecopolymer rubber; an unsaturated nitrile/conjugated diene/ethylenicallyunsaturated monomer terpolymer rubber; a rubber obtained byhydrogenating the conjugated diene units of the terpolymer rubber; or anunsaturated nitrile/ethylenically unsaturated monomer copolymer rubber.These nitrile group-containing highly saturated polymer rubbers areobtained by ordinary polymerization techniques and ordinaryhydrogenation methods. Needless to say, the method of producing theabove rubber is not particularly limited in this invention.

Some examples of the monomers used for producing the nitrilegroup-containing highly saturated rubbers in accordance with thisinvention are given below.

The unsaturated nitrile may be, for example, acrylonitrile ormethacrylonitrile.

The conjugated diene may be, for example, 1,3-butadiene,2,5-dimethylbutadiene, isoprene, or 1,3-pentadiene.

Examples of the ethylenically unsaturated monomers include unsaturatedcarboxylic acids such as acrylic acid, methacrylic acid, itaconic acidand maleic acid and salts thereof; esters of the aforesaid unsaturatedcarboxylic acids such as methyl acrylate, ethyl acrylate, butylacrylate, 2-ethylhexyl acrylate, trifluoroethyl acrylate andtrifluoroethyl methacrylate; alkoxyalkyl esters of the aforesaidunsaturated carboxylic acids such as methoxymethyl acrylate, ethoxyethylacrylate and methoxyethoxyethyl acrylate; acrylamide and methacrylamide;N-substituted (meth)acrylamides such as N-methylol (meth)acrylamide,N,N'-dimethylol (meth)acrylamide and N-ethoxymethyl (meth)acrylamide;cyanoalkyl (meth)acrylates such as cyanomethyl (meth)acrylate,2-cyanoethyl (meth)acrylate, 1-cyanopropyl (meth)acrylate,2-ethyl-6-cyanohexyl (meth)acrylate and 3-cyanopropyl acrylate; andvinylpyridine.

In preparing the unsaturated nitrile/ethylenically unsaturated monomercopolymer rubber, part of the unsaturated monomer may be replaced by anon-conjugated diene such as vinylnorbornene, dicyclopentadiene and1,4-hexadiene.

The content of the unsaturated nitrile units in the nitrilegroup-containing highly saturated rubber is usually selected within therange of 10 to 60% by weight in view of the adhesiveness of the rubberand its compatibility with a rubber adherend although this range is notparticularly limitative.

Thus, specific examples of the nitrile group-containing highly saturatedrubber constituting the latex are hydrogenation products ofbutadiene/acrylonitrile copolymer rubber,isoprene/butadiene/acrylonitrile copolymer rubber andisoprene/acrylonitrile copolymer rubber; butadiene/methylacrylate/acrylonitrile copolymer rubber and butadiene/acrylicacid/acrylonitrile copolymer rubber and hydrogenation products of theserubbers; and butadiene/ethylene/acrylonitrile copolymer rubber, butylacrylate/ethoxyethyl acrylate/vinyl chloroacetate/acrylonitrilecopolymer rubber and butyl acrylate/ethoxyethylacrylate/vinylnorbornene/acrylonitrile copolymer rubber.

The nitrile group-containing highly saturated rubber latex used in thisinvention is produced by a known phase inversion method if the rubber isa hydrogenated rubber, or by an ordinary emulsion polymerization methodif the rubber is not hydrogenated.

According to the phase inversion method, a latex of the nitrilegroup-containing highly saturated rubber can be obtained by mixing asolution of the nitrile group-containing highly saturated rubber with anaqueous solution of an emulsifier, strongly stirring the mixture toemulsify and disperse the rubber in water as fine particles, andremoving the solvent.

The solvent may be those which can dissolve the rubber, for example anaromatic solvent such as benzene, toluene or xylene, a halogenatedhydrocarbon solvent such as dichloroethane and chloroform, or a ketonesuch as methyl ethyl ketone, acetone or tetrahydrofuran.

The emulsifier used in the aqueous solution of the emulsifier may be anyof those generally known, for example potassium or sodium salts of fattyacids (e.g., olefinic acid or stearic acid), rosin acid,alkylbenzenesulfonic acids and alkylsulfuric acid esters, and nonionicemulsifiers of the polyoxyethylene type. They may be used either singlyor in combination.

The adhesive of this invention is obtained by mixing the above nitrilegroup-containing highly saturated rubber latex with theresorcinol-formaldehyde resin. The resorcinol-formaldehyde resin may beany type previously known (for example, the one disclosed in JapaneseLaid-Open Patent Publication No. 142635/1980), and there is noparticular limitation. Usually, the ratio of resorcinol and formaldehydeis preferably 1:0.5-3, more preferably 1:1-2, by weight.

In place of the resorcinol-formaldehyde resin, resorcinol-chlorophenol[such as 2,6-bis(2,4-dihydroxyphenylmethyl)-4-chlorphenol]-formaldehyderesin (e.g., "Vulcabond E" made by ICI) may be used, or a combination ofthese may be used.

Where the fibers are glass fibers, the weight ratio of theresorcinol-formaldehyde resin to the nitrile group-containing highlysaturated rubber latex (solids) is preferably 1:5-15, more preferably1:8-13. In the case of organic synthetic fibers, the above weight ratiois preferably 1:3-10, more preferably 1:5-8.

In the adhesive of this invention, part of the rubber latex may bereplaced by at least one of styrene/butadiene copolymer rubber latex, amodified product thereof, acrylonitrile/butadiene copolymer rubberlatex, a modified product thereof, natural rubber latex, etc. in amountswhich do not impair the essence of the present invention.

The amount of the adhesive to be coated is preferably 10 to 25% byweight, more preferably 15 to 20% by weight, for glass fibers, andpreferably 3 to 10% by weight, more preferably 5 to 8% by weight, fororganic synthetic fibers.

After the adhesive of this invention is applied to the fibers inpredetermined amounts, the coated fibers are heat-treated at 120° to350° C., preferably 200° to 300° C. for the glass fibers and 140° to250° C. for the organic synthetic fibers.

For some types of fibers, it is possible to immerse the fibers in asolution of an isocyanate, a solution of an epoxy compound or a mixturethereof and then dry them before they are immersed in the abovementionedtreating solution. In this case, the drying temperature is desirablybelow the temperature of the subsequent heat-treatment.

The adhesive of this invention may, as required, contain a filler suchas carbon black, a vulcanizing agent or a vulcanization accelerator.

The organic synthetic fibers which can be bonded by using the adhesiveof this invention may be, for example, polyvinyl alcohol fibers (e.g.,Vinylon fibers), polyester fibers and polyamide fibers [e.g., nylonfibers or aramid fibers (aromatic polyamide fibers)]. These organicsynthetic fibers and glass fibers may be used in the form of staples,filaments, cords, ropes and canvas.

The nitrile group-containing highly saturated rubber to be bonded to theglass fibers or organic fibers in this invention is composed of the samemonomeric units as the nitrile group-containing highly saturated rubberconstituting the above rubber latex. The content of unsaturated nitrileunits is usually 10 to 60% by weight in view of the oil resistance of arubber product obtained by bonding the rubber to the fibers. The iodinenumber of the highly saturated rubber is not more than 120, preferably 0to 100, more preferably 0 to 80, in view of the heat resistance of thefinal rubber product.

Bonding of the rubber to the fibers using the adhesive of this inventioncan be achieved by combining the above adhesive-applied heat-treatedfibers with a rubber compound prepared by adding compounding agents suchas a vulcanizer or a filler to the rubber, and subjecting the resultingcomposite to a vulcanization treatment.

The adhesive of this invention gives higher initial adhesion strengththan the conventional adhesives, and provides a striking improvement inadhesion strength after heat aging over the case of using theconventional adhesives. The adhesive of this invention can therefore beused advantageously to produce various belts such as timing belts andV-belts, various hoses such as high pressure hydraulic hoses and Freonhoses, and diaphragms in which glass fibers or organic synthetic fibersare used as a tension member.

The following examples illustrate the present invention without anyintention of limiting the scope of the invention thereby. In thefollowing examples, all parts and percentages are by weight.

SAMPLE PREPARATION EXAMPLE 1 Preparation of nitrile group-containinghighly saturated rubbers

Acrylonitrile/butadiene copolymer rubber (NBR) andacrylonitrile/butadiene/butyl acrylate terpolymer rubber obtained byemulsion polymerization were each dissolved in methyl isobutyl ketone,and each hydrogenated using a Pd-carbon catalyst to prepare hydrogenatedNBR and hydrogenated acrylonitrile/butadiene/butyl acrylate terpolymerrubber having the iodine numbers indicated in Table 1.

                  TABLE 1                                                         ______________________________________                                                 Rubber                                                                                           Acrylonitrile/                                                                butadiene/butyl                                            Acrylonitrile/butadiene                                                                          acrylate co-                                               copolymer rubber   polymer rubber                                                                     e                                            Composition                                                                            a      b      c    d    (*)  f    g    h                             ______________________________________                                        Bound     37    37     45    37   33  35   35   35                            acrylonitrile                                                                 (wt. %)                                                                       Butyl    --     --     --   --   --   60   35   35                            acrylate unit                                                                 portion                                                                       (wt. %)                                                                       Iodine   103    51     25   159  308  23   138  23                            number                                                                        ______________________________________                                         (*) Nonhydrogenated NBR.                                                 

SAMPLE PREPARATION EXAMPLE 2 Preparation of latices

Each of the samples (24.6 g) shown in Table 1 was dissolved in a mixtureof toluene and dichloroethane (75:25 by volume), and the solution waspoured into an aqueous emulsifier solution composed of 1.2 g ofpotassium oleate, 1.2 g of potassium rosinate, 0.045 g of potassiumhydroxide and 300 g of water with stirring, and the mixture wasintensely stirred at room temperature by a TK-homomixer (model M made byTokushu Kika Kogyo K. K.) at a rate of 10,000 revolutions/min. for 10minutes. The solvent was removed from the emulsifier solution by steamstripping, and the residue was concentrated by an evaporator to obtain alatex having a solid content of about 30%. It was then centrifuged atroom temperature at a rate of 3,000 revolutions/min. for 15 minutes toremove the excess of the emulsifier and effect concentration. The solidscontent and pH of the resulting latex are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Latex A       B      C    D     E    F     G    H                             Rubber                                                                              a       b      c    d     e    f     g    h                             Solids                                                                              45.3    45.5   45.0 45.0  45.4 45.0  45.4 45.6                          content                                                                       (%)                                                                           pH    9.3     9.5    9.2  9.0   9.3  9.2   9.3  9.3                           ______________________________________                                    

SAMPLE PREPARATION EXAMPLE 3 Preparation of rubber compound sheets

In accordance with the compounding recipe shown in Table 3, each of thenitrile group-containing highly saturated rubbers was kneaded with thecompounding agents as shown in Table 3 on a roll to prepare a rubbercompound sheet having a thickness of about 3 mm.

                  TABLE 3                                                         ______________________________________                                                        Rubber compound No. (parts)                                   Compounding recipe                                                                            I         II      III                                         ______________________________________                                        Zetpol 2020 (*1)                                                                              100       100     --                                          Zetpol 2000 (*2)                                                                              --        --      100                                         Zinc oxide (#1) 5         5       5                                           Stearic acid    1         1       --                                          SRF carbon black                                                                              40        50      50                                          Sulfur          0.5       0.5     --                                          Thiokol TP95 (*3)                                                                             5         --      --                                          Tetramethylthiuram                                                                            1.5       1.5     --                                          disulfide                                                                     Mercaptobenzothiazole                                                                         --        0.5     --                                          N-cyclohexyl-2-benzo-                                                                         1.0       --      --                                          thiazole sulfenamide                                                          Peroximon F040 (*4)                                                                           --        6       --                                          ______________________________________                                         Note                                                                          (*1)a product of Nippon Zeon Co., Ltd. (hydrogenated NBR, iodine number       28, bound acrylonitrile 36%)                                                  (*2)a product of Nippon Zeon Co., Ltd. (hydrogenated NBR, iodine number 4     bound acrylonitrile 36%)                                                      (*3)a highmolecular-weight polyether plasticizer (a product of                TorayThiokol Co., Ltd.)                                                       (*4)α,α'-bis-t-butylperoxide of m,pdiisopropylbenzene (a          product of Nippon Oils and Fats Co., Ltd.)                               

EXAMPLE 1

An adhesive was prepared from latex B and an aqueous solution (solidscontent 6%) of resorcinol (R)-formaldehyde (F) condensate (R/F=1/1.5) inaccordance with the following recipe.

    ______________________________________                                        Aqueous solution of resorcinol-                                                                    100 parts                                                formaldehyde condensate                                                       Latex B              135 parts                                                Water                 25 parts                                                ______________________________________                                    

The adhesive was coated on glass fiber strands (filament diameter 9micrometers; count 150 yards/pound) to a solids pick-up of 18%, and thecoated glass strands were heat-treated at 250' C. for 1 minute. Apredetermined number of the treated strands were twisted together toobtain rubber reinforcing glass fiber cords (A).

The glass fiber cords (A) was evaluated by subjecting it to a test foran adhesion to the rubber compound sheet (I) shown in Table 3 in theinitial stage and after heat aging.

The rubber compound sheet (I) was placed on the glass fiber cords, andthe entire assembly was pressured at 150° C. for 30 minutes to producean adherent sample composed of the glass fiber cords and the rubbercompound sheet. The adhesion strengths of the sample before heat aging,and after heat aging for 1 to 10 days at 130° C. were measured (180°peel test at a pulling speed of 50 mm/min.)

For comparison, an adhesive was prepared in accordance with thefollowing recipe.

    ______________________________________                                        Aqueous solution of resorcinol-                                                                     100 parts                                               formaldehyde condensate                                                       (R/F = 1/1.5; solids content 6%)                                              SBR latex (NIPOL LX110 produced                                                                     75 parts                                                by Nippon Zeon Co., Ltd.)                                                     Vinylpyridine/styrene/butadiene                                                                     75 parts                                                copolymer latex (NIPOL 2518FS                                                 produced by Nippon Zeon Co.,                                                  Ltd.)                                                                         Water                 25 parts                                                ______________________________________                                    

The adhesive was coated on glass fiber strands (filament diameter 9micrometers; count 150 yards/pound) to a solids pick-up of 18%, and thecoated glass strands were heat-treated at 250° C. for 1 minute. Threetreated strands were doubled and twisted (2.0 turns/inch) and 13 suchstrands were doubled and twisted (2.0 turns/inch) in the reversedirection to obtain rubber reinforcing glass fiber cords (B).

The rubber compound (I) was dissolved to a concentration of 15% in amixed solvent composed of 80 parts of methyl ethyl ketone and 20 partsof toluene. The resulting rubber paste was coated on the above glassfiber cords (B) to a solids pick-up of 2%, and dried at roomtemperatures. The coated fiber cords (B) were then heat-treated at 120°C. for 5 minutes to prepare glass fiber cords (C).

The glass fiber cords were evaluated in the same way as above, and theresults are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Run     Glass   Adhesion strength (kg f/25 mm) after                          No.     fiber   heat-treatment for the days indicated                         (*)     cords   0        1    3      6    10                                  ______________________________________                                        1       A       19.5     18.0 18.0   17.5 17.0                                2       B       2.0      less less   less less                                                         than than   than than                                                          1.0  1.0    1.0  1.0                                3       C       20.0     16.5 15.0   13.0 12.0                                ______________________________________                                         (*)Run No. 1 is the invention, and Runs Nos. 2 and 3 are comparisons.    

EXAMPLE 2

According to the recipe shown in Table 5, adhesives (RFL solutions) wereprepared by mixing the latices A to H indicated in Table 2 with theresorcinol-formaldehyde (RF) resin.

                  TABLE 5                                                         ______________________________________                                        RF solution             RFL solution                                          ______________________________________                                        Resorcinol   11.0       Latex     222.2                                       Formalin (37%)                                                                             6.0        RF solution                                                                             256.0                                       NaOH (10%)   3.0        Water     106.8                                       Water       246.0       Total     585.0                                       Total       256.0                                                             ______________________________________                                    

Nylon fiber cords (nylon 6, structure 1260D/2) were immersed in theadhesive prepared as above, and then heat-treated at 200° C. for 2minutes. The treated cords were held by sheets of the rubber compound(II) or (III) indicated in Table 3 to prepare a sample for a cordpulling test (H test in accordance with ASTM D2138-72). This sample wascured at 160° C. for 20 minutes in the case of the rubber compound (II)and at 170° C. for 20 minutes in the case of the rubber compound (III).To determine the cord pulling strength of the sample after aging, thesample was subjected to an air heat aging test at 120° C. for 2 weeks,and the adhesion strengths in the initial stage and after heat agingwere measured, and the results are shown in Table 4.

                                      TABLE 6                                     __________________________________________________________________________    Run    Invention            Comparison                                        No.    4  5  6  7  8  9  10 11 12 13                                          __________________________________________________________________________    Latex  A  B  C  F  H  B  H  D  E  G                                           Rubber II II II II II III                                                                              III                                                                              II II II                                          compound                                                                      Adhesion                                                                      strength                                                                      (kg/cm)                                                                       Initial                                                                              18.3                                                                             20.1                                                                             16.1                                                                             19.4                                                                             17.2                                                                             16.9                                                                             16.3                                                                             9.1                                                                              8.5                                                                              8.9                                         After heat                                                                           16.9                                                                             18.8                                                                             14.3                                                                             18.1                                                                             15.8                                                                             14.7                                                                             14.1                                                                             6.0                                                                              5.3                                                                              5.8                                         aging                                                                         __________________________________________________________________________

EXAMPLE 3

Aramid fiber cords (Kevlar produced by E. I. du Pont de Nemours & Co.;structure 1500 D/2, 127T/m) were immersed in the pre-testing liquorshown in Table 7, and then in an adhesive prepared in accordance withthe recipe shown in Table 8 from the latex shown in Table 8, and thenheat-treated at 250° C. for 1 minute. The treated cords were held bysheets of the rubber compound (II) or (III) indicated in Table 3 and asample for a cord pulling test was prepared in the same way as inExample 2. The sample was subjected to the same cord pulling test, andthe results are shown in Table 9.

                  TABLE 7                                                         ______________________________________                                        Composition of the pretreating liquor for                                     the aramid fibers                                                             ______________________________________                                        Glycerol diglycidyl ether                                                                             2.22    parts                                         10% aqueous NaOH solution                                                                             0.28    part                                          5% "AEROSOL" OT (75% solids)                                                                          0.56    part                                          (*5)                                                                          Water                   96.94   parts                                         Total                   100.00                                                ______________________________________                                         (*5)a product of Japan Aerosil Co., Ltd.                                 

                  TABLE 8                                                         ______________________________________                                        Composition (parts) of the adhesive (RFL                                      solution) for the aramid fibers                                               RF solution             RFL solution                                          ______________________________________                                        Resorcinol   11.0       Latex     185                                         Formalin     5.0        RF solution                                                                             250                                         Aqueous NaOH                                                                               3.0        Water      65                                         solution                Total     500                                         Water       231.0                                                             Total       250.0                                                             ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Run     Invention          Comparison                                         No.     14      15     16     17   18    19  20                               ______________________________________                                        Latex   B       C      H      B    E     E   G                                Rubber  II      II     II     III  II    III II                               compound                                                                      Adhesion                                                                      strength                                                                      (kg/cm)                                                                       Initial 21.6    19.8   18.9   21.3 8.8   7.1 8.3                              After   20.3    18.0   17.4   19.6 5.6   5.0 5.1                              heat                                                                          aging                                                                         ______________________________________                                    

Polyester fiber cords (polyethylene terephthalate, structure 1500 D/2)were immersed in the pre-treating solution shown in Table 10,heat-treated at 235° C. for 2 minutes, further immersed in the adhesiveprepared in Example 2, and then heat-treated at 235° C. for 2 minutes.

The treated cords were held by sheets of the rubber compound (II) or(III), and a sample for the cord pulling test was prepared. The samplewas vulcanized at 160° C. for 20 minutes, and its adhesion strength wasmeasured before and after heat aging. The results are shown in Table 11.

                  TABLE 10                                                        ______________________________________                                        Composition of the pre-treating solution for                                  the polyester fibers                                                          ______________________________________                                        Solution (L)                                                                  DENACOL EX-611 (*6) 6 parts                                                   NEOCOL SW-30 (30%) (*7)                                                                           4 parts                                                   Water               805 parts                                                 Solution (2)                                                                  CORONATE 2503 (*8)  14 parts                                                  NEOCOL SW-30 (30%)  4 parts                                                   Water               42 parts                                                  Total               875 parts                                                 ______________________________________                                         The solutions (1) and (2) were mixed to form the pretreating solution.        (*6) Sorbitol polyglycidyl ether (produced by Nagase Sangyo K. K.)            (*7) Dioctyl sulfosuccinate Na salt (produced by Daiichi Kogyo Seiyaku K.     K.)                                                                           (*8) Phenolblocked 4,4'-diphenylmethane diisocyanate (produced by Japan       Polyurethane Co., Ltd.)                                                  

                  TABLE 11                                                        ______________________________________                                        Run     Invention          Comparison                                         No.     21      22     23     24   25    26  27                               ______________________________________                                        Latex   B       C      H      B    E     E   G                                Rubber  II      II     II     III  II    III II                               compound                                                                      Adhesion                                                                      strength                                                                      (kg/cm)                                                                       Initial 23.1    20.3   20.8   22.2 10.3  8.4 9.8                              After   21.3    18.1   18.8   20.6  6.6  5.8 6.1                              heat                                                                          aging                                                                         ______________________________________                                    

What we claim is:
 1. Glass fibers which are effective for reinforcingnitrile group-containing highly saturated rubbers, said fibers beingcoated with an adhesive useful for bonding a nitrile group-containinghighly saturated rubber to glass fibers, said adhesive comprising alatex of a nitrile group-containing highly saturated rubber having aniodine number of not more than 120 and a resorcinol-formaldehyde resin.2. The glass fibers of claim 1 wherein the nitrile group-containinghighly saturated rubber of said latex is an unsaturatednitrile/conjugated diene/ethylenically unsaturated monomer terpolymerrubber.
 3. The glass fibers of claim 2 wherein in said terpolymerrubber, the nitrile is acrylonitrile or methacrylonitrile, theconjugated diene is 1,3-butadiene, 2,5-dimethylbutadiene, isoprene or1,3-pentadiene, and the ethylenically unsaturated monomer is anunsaturated carboxylic acid, an ester of an unsaturated carboxylic acid,acrylamide, methacrylamide, N-substituted (meth)acrylamide,cyanoalkyl(meth)acrylate or vinylpyridine.
 4. The glass fibers of claim1 wherein the nitrile group-containing highly unsaturated rubber of saidlatex has from 10 to 60% by weight of unsaturated nitrile units.
 5. Theglass fibers of claim 1 wherein said nitrile group-containing highlyunsaturated rubber of said latex is selected from the group consistingof acrylonitrile/butadiene/butlyacrylate copolymer rubber,butadiene/methylacrylate/acrylonitrile copolymer rubber,butadiene/acrylic acid/acrylonitrile copolymer rubber, hydrogenationproducts of these rubbers, and butadiene/ethylene/acrylonitrilecopolymer rubber.
 6. The glass fibers of claim 1 wherein saidresorcinol-formaldehyde resin has a ratio of resorcinol and formaldehydeof from 1:0.5 to 1:3.
 7. The glass fibers of claim 1 wherein saidresorcinol-formaldehyde resin has a ratio of resorcinol and formaldehydeof from 1:1 to 1:2.
 8. The glass fibers of claim 1 wherein the weightratio of the resorcinol-formaldehyde resin to the nitrilegroup-containing highly saturated rubber latex is from 1:5 to 1:15. 9.The glass fibers of claim 1 wherein the weight ratio of theresorcinol-formaldehyde resin to the nitrile group-containing highlysaturated rubber latex is from 1:3 to 1:10.